Pulmonary epithelial-myoepithelial carcinoma with high-grade transformation in a cat.

[CASE SUMMARY] A 14-year-old spayed female Scottish Fold cat was presented to a private veterinary clinic for a health check. Radiography revealed a nodule measuring 1.0 cm diameter in the cranial segment of the cranial lobe of the left lung. On day 12, non-contrast-enhanced CT revealed a well-defined pulmonary nodule measuring 1.7 cm in diameter in the same area. On day 48, the nodule in the cranial segment of the left cranial lobe was resected by lobectomy. The nodule was firm and pale pink in surface colour. Microscopically, the mass was adjacent to the bronchi and bronchial glands and was composed of luminal cells forming the duct structure and an outer layer of non-luminal cells with squamoid differentiation. Tumour cells partially invaded into the surrounding parenchyma. Immunohistochemically, the luminal cells were positive for cytokeratin (CK) AE1/AE3, CK7, CK19, thyroid transcription factor-1 and human epidermal growth factor 2. Non-luminal cells were positive for CK AE1/AE3, p63, calponin, smooth muscle actin and p40. The Ki-67 indices of the luminal and non-luminal cells were 10.4% and 12.8%, respectively. Based on these findings, the tumour was diagnosed as a pulmonary epithelial-myoepithelial carcinoma with high-grade transformation as defined in the human World Health Organization classification.

[RELEVANCE AND NOVEL INFORMATION] This is the first report of pulmonary epithelial-myoepithelial carcinoma with high-grade transformation characterised by morphology and immunohistochemistry.